Cathode having electron production and focusing grooves, ion source and related method

ABSTRACT

A cathode having electron production and focusing grooves for an ion source of an ion implanter system, the ion source and a related method are disclosed. In one embodiment, the cathode includes a working surface having a plurality of electron production and focusing grooves positioned therein. A repeller of the ion source may be similarly structured.

BACKGROUND

1. Technical Field

The disclosure relates generally to ion implantation, and moreparticularly, to a cathode having electron production and focusinggrooves for an ion source of an ion implanter, the ion source and arelated method.

2. Background Art

A cathode and a repeller are positioned within an ion source of an ionimplanter to generate an ion plasma by injecting electrons into a sourcegas. The repeller is at the same potential as the cathode but is notheated—its purpose is to prevent electrons escaping the plasma byreflecting them back into the plasma. When installed, the cathode andrepeller both present a substantially planar working surface to thesource gas. However, as the ion source is used, their working surfaceserode to have a concave surface, especially that of the cathode. Theconcave surface acts to increase the output of the ion source,particularly as the cathode approaches the end of its useful life. Inparticular, the concave surface of the cathode focuses the thermionicelectrons in a central region of the plasma, which increases output.Unfortunately, the duration of the increased output is limited due tothe cathode reaching the end of its useful life.

One approach to take advantage of the increased output is to build acathode having a concave surface. This approach, however, is not tenablefor a number of reasons. First, the concave surface cathode may reducethe lifetime of the cathode due to the thinner center. Typically,failure occurs at the center of the cathode. Furthermore, the concavesurface cathode may require structure that presents a higher thermalmass, which is difficult to heat and control, e.g., if the edges of thecathode surface are thicker.

SUMMARY

A cathode having electron production and focusing grooves for an ionsource of an ion implanter system, the ion source and a related methodare disclosed. In one embodiment, the cathode includes a working surfacehaving a plurality of electron production and focusing groovespositioned therein. A repeller of the ion source may be similarlystructured.

A first aspect of the disclosure provides a cathode for an ion source ofan ion implanter, the cathode comprising: a working surface having aplurality of electron production and focusing grooves positionedtherein.

A second aspect of the disclosure provides an ion source for an ionimplanter, the ion source comprising: a source gas inlet; a cathodecomprising a working surface having a plurality of electron productionand focusing grooves positioned therein; and an ion plasma outlet.

A third aspect of the disclosure provides a method of generating an ionplasma, the method comprising: providing a source gas; applying a biason a cathode adjacent to the source gas to generate the ion plasma, thecathode comprising a working surface having a plurality of electronproduction and focusing grooves positioned therein.

The illustrative aspects of the present disclosure are designed to solvethe problems herein described and/or other problems not discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the disclosure taken in conjunction with the accompanyingdrawings that depict various embodiments of the disclosure, in which:

FIG. 1 shows a schematic view of an ion implanter system according tothe disclosure.

FIG. 2 shows a cross-sectional side view of an ion source according tothe disclosure.

FIG. 3 shows a top view of the ion source of FIG. 2 with an ion plasmaoutlet cover removed.

FIG. 4 shows an isometric view of a cathode according to the disclosure.

FIG. 5 shows a partial cross-sectional view of the cathode of FIG. 4.

FIG. 6 shows a top view of an alternative embodiment of the cathode ofFIGS. 4-5.

FIG. 7 shows a partial cross-sectional view of an alternative embodimentof the cathode of FIGS. 4-6.

It is noted that the drawings of the disclosure are not to scale. Thedrawings are intended to depict only typical aspects of the disclosure,and therefore should not be considered as limiting the scope of thedisclosure. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION

A cathode for an ion source, the ion source and a related method aredisclosed. As an introduction, FIG. 1 shows an illustrative ionimplanter system 100 according to the disclosure. Implanter system 100includes an ion beam generator 102 for generating and transmitting anion beam 104 to a target 106 in an implant chamber 108. Ion beamgenerator 102 may be any now known or later developed ion beam generatorsuch as those available from Varian Semiconductor Equipment Associates.Typically, target 106 includes one or more semiconductor wafers mountedto a platen 114. Characteristics of platen 114 and, hence, target 106,may be controlled by a platen drive assembly 116 that rotates the target106, i.e., wafer, and a target vertical scan system position controller118 that controls the vertical position of target 106. Drive assembly116 and position controller 118 are both responsive to a systemcontroller 120.

Besides the above-described components, ion beam generator 102 mayinclude a gas flow 140; an ion source 142 including a source magnet 144and a source bias voltage controller 146; a suppression electrode 148,an extraction electrode 150 and one or more manipulator motors 152 forelectrodes 148, 150; an analyzer magnet 154; an accelerator focuselectrode 156; an accelerator suppression electrode 158; a mass slit160; a pre-scan suppression electrode 162; horizontal scan plates 164; apost-scan suppression electrode 166; a nitrogen (N₂) bleed 168; acorrector magnet 170; a limiting aperture 172; and a profiler system112. Each of the above-described components is monitored by andresponsive to system controller 120. Since operation of ion implantersystem 100 is known, no further details are described herein.

Turning to ion source 142, according to one embodiment of thedisclosure, as shown in FIGS. 2-3, ion source 142 includes a source gasinlet 200, e.g., coupled to gas flow 140 (FIG. 1), and an ion plasmaoutlet 202 (FIG. 2 only) in a cover 204. FIG. 2 shows a cross-sectionalside view and FIG. 3 shows a top view with an ion plasma outlet coverremoved. Ion source 142 also includes a cathode 210 and a repeller 212for applying a bias to gas entering ion source 142 to create an ionplasma (not shown) that exits via ion plasma outlet 202.

As shown best in FIGS. 4 and 5, cathode 210 includes a working surface214 having a plurality of electron production and focusing grooves 216positioned therein. In FIGS. 4-5, electron production and focusinggrooves 216 constitute substantially concentric grooves. A mount 215 iscoupled to a back side of working surface 214 for coupling to a clamp217 (FIG. 2) of ion source 142 (FIG. 2). FIG. 5 shows a partialcross-sectional view of cathode 210. Each of the plurality of electronproduction and focusing grooves 216 includes an angled surface 218angled relative to a planar portion 220 of working surface 214. As shownin FIG. 2, angled surface 218 of each groove 216 faces a focal point FPat a distance D from working surface 214. That is, lines extendingsubstantially perpendicular from each angled surface 218 intersect atfocal point FP. Focal point FP may be adjacent to ion plasma outlet 202.In one embodiment, the angle of angled surface 218 of each groove 216may be different, for example, such that they all face focal point FP,or to ensure angled surfaces 218 face focal point FP for the longestduration possible as cathode 210 ages. However, this is not necessary asthe angle of angled surface 218 of each groove 216 may be substantiallyidentical, e.g., for ease of manufacture. In addition, angled surfaces218 need not be planar, as shown, and other arrangements (e.g., concave)that focus the plasma being generated may also be employed. In oneembodiment, distance D may be approximately 30 mm from working surface214. Of course, this distance may change depending on the dimensions ofion source 142.

FIG. 6 shows an alternative embodiment in which electron production andfocusing grooves 216 are not positioned in a substantially concentricmanner, i.e., are not circular, and are discontinuous. Nonetheless,electron production and focusing grooves 216 of FIG. 6 providesubstantially similar benefits as described herein. Although FIGS. 4-6show a certain number of grooves 216, e.g., 3, it is understood that anynumber of grooves may be employed.

In FIGS. 4 and 5, working surface 214 has a substantially uniformthickness. That is, other than grooves 216, the thickness is the same.Hence, the overall working surface has a substantially uniformthickness. FIG. 7 shows an alternative embodiment in which a centralregion 230 of working surface 214 is thicker than an outer region 232 ofworking surface 214.

Returning to FIG. 2, ion source 142 may also include a repeller 212having substantially similar structure to cathode 210. That is, repeller212 may have a working surface 314 having a plurality of electronfocusing grooves 316 positioned therein. Each of grooves 316 of repeller212 includes an angled surface 318 angled relative to a planar portion320 of working surface 314 of repeller 212. In this case, angled surface218, 318 of each groove 216, 316 may face focal point FP at distance Dfrom working surfaces 214, 314 of cathode 210 and repeller 212.

In operation, an ion plasma 250 (FIG. 2) is generated using ion source142. In particular, a source gas is provided via gas flow 140 (FIG. 1)to ion source 142. A bias is applied on cathode 210 adjacent to thesource gas to generate the ion plasma. A bias is also applied onrepeller 212 adjacent to the source gas so as to repel the electrons. Inone embodiment, repeller 212 and cathode 210 are at the same potential,but this is not essential. Working surface 214 focuses the thermionicelectrons in a central region of ion plasma 250, which increases outputas if the working surface was concave. In this fashion, cathode 210 actssimilarly to the Fresnel type of lens used in optical systems. However,cathode 210 does not suffer from a substantially thinner working surface214 (as with an aging, initially-planar cathode), which would shortenit's life cycle. Cathode 210 may provide increased output in the rangeof approximately 40-50% compared to that of a perfectly planar cathodeat the start of use. As cathode 210 is used, it will become concave,with the depth of grooves 216 diminishing over time.

The foregoing description of various aspects of the disclosure has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the disclosure to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to aperson skilled in the art are intended to be included within the scopeof the disclosure as defined by the accompanying claims.

1. A cathode for an ion source of an ion implanter, the cathodecomprising: a working surface having a plurality of electron productionand focusing grooves positioned therein.
 2. The cathode of claim 1,wherein the plurality of electron production and focusing groovesincludes a plurality of substantially concentric grooves.
 3. The cathodeof claim 1, wherein each of the plurality of grooves includes an angledsurface angled relative to a planar portion of the working surface. 4.The cathode of claim 3, wherein the angle of the angled surface of eachof the plurality of the grooves is substantially identical.
 5. Thecathode of claim 3, wherein the angled surface of each of the pluralityof the grooves faces a focal point at a distance from the workingsurface.
 6. The cathode of claim 5, wherein the distance isapproximately 30 mm from the working surface.
 7. The cathode of claim 1,wherein a central region of the working surface is thicker than an outerregion of the working surface.
 8. The cathode of claim 1, wherein theworking surface has a substantially uniform thickness.
 9. An ion sourcefor an ion implanter, the ion source comprising: a source gas inlet; acathode comprising a working surface having a plurality of electronproduction and focusing grooves positioned therein; and an ion plasmaoutlet.
 10. The ion source of claim 9, wherein the plurality of electronproduction and focusing grooves includes a plurality of substantiallyconcentric grooves.
 11. The ion source of claim 9, wherein each of theplurality of electron production and focusing grooves includes an angledsurface angled relative to a planar portion of the working surface. 12.The ion source of claim 11, wherein the angle of the angled surface ofeach of the plurality of the grooves is substantially identical.
 13. Theion source of claim 11, wherein the angled surface of each of theplurality of the grooves faces a focal point at a distance from theworking surface.
 14. The ion source of claim 13, wherein the distance isapproximately 30 mm from the working surface.
 15. The ion source ofclaim 13, further comprising an output aperture, wherein the focal pointis adjacent to the output aperture.
 16. The ion source of claim 9,wherein a central region of the working surface is thicker than an outerregion of the working surface.
 17. The ion source of claim 9, whereinthe working surface has a substantially uniform thickness.
 18. The ionsource of claim 9, further comprising a repeller having a workingsurface having a plurality of electron production and focusing groovespositioned therein.
 19. The ion source of claim 18, wherein each of theplurality of electron production and focusing grooves of the cathodeincludes an angled surface angled relative to a planar portion of theworking surface of the cathode, and each of the plurality of electronfocusing grooves of the repeller includes an angled surface angledrelative to a planar portion of the working surface of the repeller. 20.The ion source of claim 19, wherein the angled surface of each of theplurality of the electron production and focusing grooves faces a focalpoint at a distance from the working surfaces of the cathode and therepeller.
 21. The ion source of claim 20, wherein the focal point isadjacent to the ion plasma outlet.
 22. An ion implanter systemcomprising the ion source of claim
 9. 23. A method of generating an ionplasma, the method comprising: providing a source gas; applying a biason a cathode adjacent to the source gas to generate the ion plasma, thecathode comprising a working surface having a plurality of electronproduction and focusing grooves positioned therein.
 24. The method ofclaim 23, wherein each of the plurality of electron production andfocusing grooves includes an angled surface angled relative to a planarportion of the working surface.
 25. The method of claim 24, wherein theangle of the angled surface of each of the plurality of the electronproduction and focusing grooves is substantially identical.
 26. Themethod of claim 24, wherein the angled surface of each of the pluralityof the grooves faces a focal point at a distance from the workingsurface.
 27. The method of claim 26, wherein the distance isapproximately 30 mm from the working surface.
 28. The method of claim23, wherein a central region of the working surface is thicker than anouter region of the working surface.
 29. The method of claim 23, whereinthe working surface has a substantially uniform thickness.
 30. Themethod of claim 23, further comprising applying a bias on a repelleradjacent to the source gas, the repeller comprising a working surfacehaving a plurality of electron focusing grooves positioned therein.